Giant space mirrors could turn night into daylight, astronomers warn

A Space.com study on Reflect Orbital’s plan to deploy space mirrors finds that a single 60-by-60-foot mirror would cast a beam roughly 3.4 miles wide that appears 40 times brighter than the full Moon to observers in its path, turning the night sky into a twilight zone and washing out stars within the beam. The glow would extend up to about 50 miles from the beam, and could brighten the sky above the horizon for many miles in the beam’s direction, depending on conditions. If 40,000 mirrors were launched, the combined light could be 10,000 times brighter than the full Moon, creating daytime-like brightness that could hinder astronomy, even as proponents tout potential uses for nighttime solar power and disaster illumination. The FCC licensed a demonstration satellite (EARENDIL-1) for this concept, prompting objections from astronomers and environmental groups; Reflect Orbital argues that only a fraction would be active and that coordination with NSF and independent researchers is planned. The debate highlights a tension between space-led lighting/testing and preserving dark skies for astronomy.